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Design of Hand-holes in tubular members - Highway signs and structures.

Kussay (Structural)
15 May 12 2:59
I have checked previous threads dealing with the subject and there was very useful comments regarding the hand-hole reinforceemnt for the bending and axial forces. However, the torsional properities of the tubular member (J) decreases drastically (maybe by a thousand fold) when any tiny cut-out is introduced. No reinforcement to the hand-hole can ever (practically) reinstate this as you can all appreciate.

I figure that:

1. For a relatively small hand-hole in a large diameter member, the torsional (any other)stresses will simply be redistributed around the hole and the issue becomes a matter stress concentration around the hole. For bending and axial forces, the hole can simply be reinforced to restore the original section properties Ax, Iz & Iy but for torsional property J which cannot be restored by reinforcement, the stress concentrations around the hand-hole will have to be assessed. I have not found any literature yet that addresses the assessment of the stress concentrations around an opening in a round hollow member (only stress concentration for plates in unitform tension with a hole are widely available).

2. As the hole gets larger in comparision with the diameter of the member (especially in the direction parallel to the member axis), the torsion becomes more and more of an issue as the shear stress re-distribution around the hand-holes becomes impossible and the member would have to resist the torsion as if it is an "open" section (e.g. like a channel) which is very poor in torsion resistance and is likely to fail in torsion. Again, for bending and axial forces, the larger hole can always be reinforced to compensate for the loss of area, Ix & Iy.

Thus short of doing a finite element analysis with a fine mesh for the member with the hand-hole, has anyone found literature that helps in the design of tubular members with hand-holes subjected to torsion?



Duwe6 (Industrial)
17 May 12 9:02
Wind-generation towers and column skirts use heavy barstock 'banding' wrapped around the ID of the opening. These work well to handle the bending and torsional stresses in the 'real world'. If I was presented [stuck] with your problem, I would add enough inch^3 of bar to 'replace the hole', just like a standard repad calc.

It's kind of a Sect. VIII Div. 1 approach: minimal calc's, and rules-of-thumb that have been proven to work.

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